1. The Field of the Invention
This invention relates to visual cut indicators for power cutting equipment in which a cutting element, such as a circular saw blade, moves along a cutting path. More particularly, the invention relates to improved power cutting equipment of the type where a visual indication of the location of the cutting path, commonly referred to as the kerf, is projected onto a workpiece to be cut by the cutting equipment.
2. The Relevant Technology
Kerf indicators allow an operator to more accurately position a workpiece in relation to a cutting element, such as a saw blade, in order to cut the workpiece. However, with conventional kerf indicators, skill and care must be exercised by the operator to cut only at the desired location on the workpiece. An operator may gain skill through experience and training, but must always take time to carefully align the workpiece before each cut is made. This time-consuming process decreases the operator's productivity and does not guarantee that a mistake will not be made. Even the most skilled operators make occasional miscuts due to the inherent difficulty of aligning the blade and workpiece.
Using conventional power cutting equipment, for example a miter saw, an operator wishing to make a cut in a workpiece must visually line up the point at which the workpiece is to be cut with a plane through which the saw blade will move. The motion of the blade is confined to this plane and the kerf will lie in this plane. Various means are used to assist the operator in aligning the workpiece and the saw blade. For example, conventional miter saws have a channel in a fence. The fence rises from a table that supports the workpiece. When the saw blade is moved through its plane of motion to make a cut, the blade passes through the channel in the fence. Consequently, the channel can be used as a rough indication of where the kerf will be made. The point at which the workpiece is to be cut can accordingly be aligned with the channel.
However, because the channel is necessarily larger than the width of the saw blade, the exact position of the cut to be made is difficult to determine with precision using only the channel as a guide. Moreover, a point at which a convoluted workpiece surface, such as the surface of molding, is to be cut may be difficult to align with the channel if the marking indicating the point to be cut is interior to the edges of the workpiece.
It becomes even more difficult to make accurate cuts with conventional equipment if the kerf is to be at an angle through the workpiece, as opposed to orthogonal. When cutting on an angle, the point at which the blade begins to cut the workpiece may appear to an operator to be spaced from the channel in a direction along the fence. This occurs because the plane through which the blade moves is at an angle as viewed by the operator. Thus, even the most experienced operator may have difficulty making an angled cut.
Furthermore, certain cutting equipment, for example radial arm saws and compound miter saws, allow adjustments of the saw blade for angular cuts by rotation in two axes. This may further increase the difficulty of alignment, and increase the time required to perform the cutting operation.
In practice, operators often bring the blade into close proximity with the workpiece to better estimate the position of the cut to be made. In some situations, operators will actually bring the blade into contact with the workpiece so that a very small portion of the workpiece is removed to indicate the kerf, a technique sometimes referred to as "nibbling." These practices take time and, in the case of nibbling, may result in workpieces that are ruined and unusable or must be repaired at an additional expense.
Attempts have been made to solve these problems by projecting a shadow using a light source positioned behind the saw blade, or behind an object such as a wire or bar aligned with the blade, to provide the necessary reference for indicating the kerf. Such devices, however, have the inherent difficulty of aligning the light source, the wire or bar etc. (if such is used) and the cutating element, to give an accurate indication of the path of the cutting element. Elaborate provisions for this alignment have been provided in prior devices, requiring precise adjustment.
Another difficulty with such shadow indicators is a lack of definition in the shadow line, i.e. the shadow line has an umbra and a penumbra. The umbra and penumbra may be so closely associated that the umbra appears to have a blurred edge, which further complicates making an accurate cut in the workpiece.
Moreover in kerf indicating device that use a light source, the light source and its housing and surrounding structure may become extremely hot. This exposes the operator to potential burn injury if he or she inadvertently touches the hot parts of the device. The danger is heightened when a high intensity light bulb such as a halogen bulb, for example, is used. Such a high intensity bulb may be required if the device is to be used outside in bright sunlight.
Additionally, in conventional devices where the shadow of the cutting element is used as a kerf indicator, only one side of the keraf is accurately indicated. For example, the shadow may shade part of the workpiece creating a more or less defined line along which the blade will cut. However, the width of the blade may cut inside or outside the shadow line, i.e. on one side or the other of the line between shadow and light. If the cut is not made on the proper side of the shadow line, the workpiece will be too short by the width of the blade. This requires additional effort on the part of the operator to determine and orient the workpiece such that the width of the kerf (i.e. the width of the blade) falls on the waste side of the mark indicating where the cut is to be made.
Other arrangements for indicating the location of a cut to be made include projecting a laser beam onto the workpiece that is aligned with the saw blade path. Unfortunately, such devices are costly, particularly for small power cutting equipment such as a miter saw or radial arm saw. In some such cases, the laser kerf indicator may constitute a significant percentage of the total cost of the saw.
Moreover, laser keraf indicators, like the shadow kerf indicators described above, indicate only one side of the kerf, forcing the operator to carefully consider on which side of the laser line the blade will pass and aligning the waste portion of the workpiece accordingly. Lasers also pose a potential threat to the eyes of an operator. If the laser used is fairly powerful, for example, a laser to be used outside in direct sunlight, and the laser is inadvertently directed into the eyes of the operator, an injury may result.
Laser kerf indicating devices face additional problems when the cutting element, such as a saw blade, is changed. The new blade may vary in width from the previous blade requiring an expensive and time-consuming adjustment to the laser. Furthermore, laser kerf indicators may require periodic adjustment due to misalignment caused by vibration of the equipment, unintentional physical shocks to the equipment, or thermal expansion of the equipment components that cause the components of the device to creep out of alignment.
Accordingly, there exists a need in the art for an improved kerf indicating device that accurately and completely indicates where the kerf will fall on the workpiece, which is inexpensive and which safeguards against injury to the operator. The present invention is directed to fulfilling this need.